Many diesel engines require both a higher pressure fuel system and a lower pressure fuel system to supply fuel for engine operation and return it back to the fuel tank. The lower pressure fuel system supplies fuel to the higher pressure fuel system, at the desired pressure, temperature, quantity and quality (cleanliness and water free), which in turn pressurizes that fuel and supplies that fuel to the engine. The lower pressure fuel system has another function; it returns unused fuel from the high pressure fuel system back into the low pressure fuel system and tank. In a higher pressure fuel system, the majority of fuel is used by the engine for combustion; however, portions of the fuel are used to cool and lubricate the high pressure pump, to actuate the high pressure engine fuel injectors, and to regulate the rail pressure via opening and closing of a control valve that is hydraulically connected to the high pressure fuel in the fuel rail. The fuel that is used for these purposes is not consumed and must be returned back into the lower pressure fuel system via a return fuel system, including return lines and ducts coupled to the lower pressure fuel system.
Several problems may arise in such a system. For example, if the injector return fuel pressure (back pressure) is not maintained, (i.e. falls below a minimum pressure) the hydraulic actuators in the injectors may collapse, keeping the injectors from actuating. The loss of the ability to inject can result in a no start or long extended cranks during cold start of the engine or poor to no operation on an already running engine. Further, return fuel may include engine debris from manufacturing and other sources, which can block the fuel lines and damage fuel pumps. Furthermore, gelling or waxing of cold fuel may block fuel lines, especially at fuel filters and fuel pumps, thus decreasing fuel supply pressure and quantity which can degrade engine performance and damage the high pressure fuel pump due to lack of lubrication. Further still, if the return pressure is too high (i.e. rises above a maximum pressure) because of blockage in the return line, the seals on the high pressure pump and/or the low pressure pump may be destroyed. Other problems that may arise include, a lack of prompt draining of a water in fuel (WIF) reservoir and changing of one piece fuel filters, which include the housing, may cause contamination of the fuel system, and the fuel system may run-dry or have air ingestion during plant priming.
One approach to address the above described problems is a multi-staged fuel return system. A multi-staged fuel return system may comprise: a fuel supply; a low pressure fuel pump coupled to the fuel supply; a first fuel filter disposed between the low pressure fuel pump and the fuel supply, the first fuel filter having a first filtration size (e.g., pore size) and being disposed a WIF reservoir with a WIF sensor; a high pressure fuel pump; a second fuel filter disposed between the high pressure fuel pump and the low pressure fuel pump, the second fuel filter having a second filtration size, the second filtration size finer than the first filtration size (e.g., pore size); a common fuel rail downstream of the high pressure fuel pump; a pressure control valve coupling the common fuel rail to a first fuel return line, the first fuel return line directing return fuel to either of the fuel supply, and a region of a low pressure fuel pump intake line, which is upstream of the first fuel filter; a second fuel return line, the second fuel return line directing return fuel from the high pressure pump to the first fuel return line; a plurality of injectors coupled to a third fuel return line, the third fuel return line directing return fuel to a region of a high pressure pump intake line between the low pressure fuel pump and the high pressure fuel pump, which is upstream of the second fuel filter.
Using the system described above, return fuel may be directed to multiple locations in a lower pressure fuel system (region upstream of the high pressure fuel pump), the fuel supply, and to the high pressure pump. In this way, fuel pressure at the various locations within the system may be more tightly regulated. Further, the system takes advantage of the heat of the return fuel to decrease gelling/waxing of fuel in fuel lines, fuel filters, and fuel pumps, and excessively hot fuel may also be diverted back to the fuel supply to mix with colder bulk fuel to prevent fuel over-temperature from damaging fuel system components. Furthermore, when cold starting the engine, initiating the pressure supplied by the low pressure fuel pump to the injector return line improves cold start performance and operation of the vehicle by providing stable pressurized fuel to the return side of the fuel injector, quickly inflating the hydraulic actuators allowing them to run quickly and consistently. Further still, the described system improves protection against contamination of the fuel system from engine debris, which could potentially cause pump failures. Additionally, high pressure that may prevent damage to pump seals can be relieved by having multiple return paths, the WIF sensor indicates when the WIF reservoir need to be drained and protects fuel from contamination during changing of the filter, and imparting low pressure pump fuel pressure on injectors enables faster air bleed during plant priming.
In another example, a multi-staged fuel return system may comprise: a fuel supply; a low pressure fuel pump coupled to the fuel supply; a first fuel filter disposed between the low pressure fuel pump and the fuel supply; a high pressure fuel pump; a second fuel filter disposed between the high pressure fuel pump and the low pressure fuel pump; a common fuel rail downstream of the high pressure fuel pump; a pressure control valve coupling the common fuel rail to a first fuel return line, the first fuel return line directing return fuel to either of the fuel supply and a low pressure fuel pump intake line at a location upstream of the first fuel filter; a plurality of injectors coupled to a second fuel return line, the second fuel return line directing return fuel to a high pressure pump intake line at a location upstream of the second fuel filter.
It should be understood that the summary above is provided to introduce, in simplified form, a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.